story-kit: done 270_bug_qa_test_server_overwrites_root_mcp_json_with_wrong_port

.story_kit/work/5_done/270_bug_qa_test_server_overwrites_root_mcp_json_with_wrong_port.md

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+---
+name: "QA test server overwrites root .mcp.json with wrong port"
+---
+
+# Bug 270: QA test server overwrites root .mcp.json with wrong port
+
+## Description
+
+When the QA agent starts a test server in a worktree (e.g. on port 3012), that server auto-detects the shared project root and calls open_project, which writes .mcp.json with the test server's port. This clobbers the root .mcp.json that should always point to the main server (port 3001).
+
+Root cause: open_project in server/src/io/fs.rs:527 unconditionally calls write_mcp_json(&p, port) with its own port. Because worktrees share .story_kit/ with the real project, the test server resolves to the real project root and overwrites the root .mcp.json instead of writing to its own worktree directory.
+
+Fix: Remove the write_mcp_json call from open_project entirely. Worktree .mcp.json files are already written correctly during worktree creation (worktree.rs:81,97), and the root .mcp.json is committed in git. open_project should not touch it.
+
+## How to Reproduce
+
+1. QA agent starts on a story\n2. QA agent starts a test server in the worktree on a non-default port (e.g. 3012)\n3. Test server auto-opens the project root\n4. Root .mcp.json is overwritten with test port
+
+## Actual Result
+
+Root .mcp.json contains the QA test server's port (e.g. 3012) instead of the main server's port (3001). Interactive Claude sessions lose MCP connectivity.
+
+## Expected Result
+
+Root .mcp.json always points to the primary server's port. Test servers started by QA agents should not overwrite it.
+
+## Acceptance Criteria
+
+- [ ] QA test servers do not overwrite root .mcp.json
+- [ ] Root .mcp.json always reflects the primary server's port
+- [ ] Worktree .mcp.json files are only written during worktree creation